Devices for dispensing foam produce the foam from a foamable liquid stored in the container using the air also stored in the container. The foam is formed by compressing the container, for example a bottle, during which process the air and liquid are forced out of the container into separate passages, fed to a mixing element for forming foam therein by mixing and conveyed to the outside. This type of foam production avoids the use of environmentally harmful propellant gases.
A conventional device which is on the market has a mounting section which is arranged in the neck of the bottle and in which a conical mixer section is clamped. The mixer section contains essentially coaxial passages for air and liquid leading to a porous mixing element and also a return channel, also coaxial with the passages, for the return of air when the pressure action on the bottle is removed. The mixing element covers the entire coaxial passage system, i.e., both the feed pipes and the return channel. Arranged on the bottle neck is a carrier for a cap which sits on the carrier, can be changed over from an open to a closed position and has a dispensing opening communicating in an open position with a foam outlet arranged above the mixing element.
This known device has various disadvantages. Foam can escape between cap carrier and cap, as a result of which the outside wall of the bottle becomes dirty and difficult to handle. The serviceability of the bottle can only be checked after it is filled so that faulty bottles or devices can only be sorted out at this stage. The secondary air returning upon removing the pressure from the bottle carries liquid back into the bottle via the mixing element, which again converts the air and liquid into foam. This returned foam fills a section of the air space in the bottle and impairs its serviceability. The known device is poorly suited to inverted removal since a so-called wet shot containing incompletely formed foam is always produced at the beginning of the removal process.